In recent years, an input detection device with a touch detection function, so-called a touch panel, capable of detecting proximity (hereinafter including contact) of an external object has drawn attention as an input detection device. The touch panel is mounted on a display device such as a liquid crystal display device or is integrated with the liquid crystal display device, and thus, the display device with a touch detection function is provided.
There is a touch panel on which a pen can be used as an example of the external object. By using the pen, for example, a small region can be designated or a handwritten character can be input. There are various techniques for detecting touch with a pen. An example of the various techniques is an electromagnetic induction method. The electromagnetic induction method is a dominant technique as a technique for detecting touch with a pen, since the electromagnetic induction method can achieve high accuracy and high pen-pressure detection accuracy and can also achieve a hovering detection function where the external object is separated from a front surface of the touch panel.
In addition, there is a touch detection device capable of detecting a finger or the like as the external object. In this case, since a detection target is not a pen, a method other than the electromagnetic induction method is adopted as the technique for detecting touch. For example, there are methods of detecting an optical change, a change in resistance value, or a change in electric field generated by touch with a finger or the like. Among these methods, an example of the methods of detecting a change in electric field is a capacitive sensing method using electrostatic capacitance. Since a relatively simple structure is used and power consumption is low in the capacitive sensing method, the capacitive sensing method is used for a personal digital assistant and the like.
A technique related to an electromagnetic induction touch panel is described, for example, in Japanese Patent Application Laid-Open Publication No. H10-49301 (Patent Document 1).